Dihydrofolate reductase binding and cellular uptake of nonpolyglutamatable antifolates: correlates of cytotoxicity toward methotrexate-sensitive and -resistant human head and neck squamous carcinoma cells.

摘要: Several mechanisms have been demonstrated to be independently involved in methotrexate (MTX) resistance, including increased dihydrofolate reductase (DHFR) activity, decreased membrane transport, and conversion noneffluxing polyglutamates by folylpolyglutamate synthetase. We conducted the present study test hypothesis that nonpolyglutamatable antifolates with an N delta-hemiphthaloyl-L-ornithine side chain could more potent than MTX against MTX-sensitive -resistant human carcinoma cells via tighter DHFR binding, efficient cellular uptake, ability bypass defective polyglutamation, or a combination. Two antifolates, alpha-(4-amino-4-deoxypteroyl)-N (PT523) new B-ring analogue alpha-[4-[N-(2,4-diamino-5-chloroquinazolin-6-yl)methyl]amino] benzoyl-N (PT619), were tested as inhibitors of purified recombinant found bind somewhat better enzyme determined competitive radioligand binding assay. PT523 PT619 9- 14-fold, respectively, active parental SCC25 neck squamous cell growth 72-hr cultures. Moreover, there was even greater increase relative potency two previously described MTX-resistant lines content convert polyglutamates: SCC25/R1 (selected MTX) SCC25/CP cisplatin but collaterally resistant MTX). Both very efficiently inhibited [3H]MTX uptake 1-hr assay, being 11-fold 17-fold MTX. Greater inhibition also observed SCC/CP cells. However, activity experiments less growth-inhibition assays, especially for This suggested additional cytotoxicity determinants may exist these